Antioxidants are the key ingredients in anticancer foods.

Cancer Prevention Foods
Anti-cancer Foods updated on November 19, 2007

Most cancer prevention (or anti-cancer) foods or diets contain are rich
sources of anti-oxidants. These antioxidants are the key elements to
lower the risk of most cancers. The key points of antioxidants are listed
as below:

Antioxidants protect cells from damage caused by unstable molecules
known as free radicals).

Laboratory and animal research has shown antioxidants help prevent
the free radical damage that is associated with cancer. However,
results from recent studies in people (clinical trials) are not
consistent .

Antioxidants are provided by a healthy diet that includes a variety of
fruits and vegetables.

What are antioxidants?
Antioxidants are substances that may protect cells from the damage
caused by unstable molecules known as free radicals. Free radical
damage may lead to cancer. Antioxidants interact with and stabilize free
radicals and may prevent some of the damage free radicals otherwise
might cause. Examples of antioxidants include beta-carotene, lycopene,
vitamins C, E, and A, and other substances.

Can antioxidants prevent cancer?
Considerable laboratory evidence from chemical, cell culture, and animal
studies indicates that antioxidants may slow or possibly prevent the
development of cancer. However, information from recent clinical trials is
less clear. In recent years, large-scale, randomized clinical trials reached
inconsistent conclusions.

What was shown in previously published large-scale
clinical trials?
Five large-scale clinical trials published in the 1990s reached differing
conclusions about the effect of antioxidants on cancer. The studies
examined the effect of beta-carotene and other antioxidants on cancer
in different patient groups. However, beta-carotene appeared to have
different effects depending upon the patient population. The conclusions
of each study are summarized below.

Â• The first large randomized trial on antioxidants and cancer risk was
the Chinese Cancer Prevention Study, published in 1993. This trial
investigated the effect of a combination of beta-carotene, vitamin E, and
selenium on cancer in healthy Chinese men and women at high risk for
gastric cancer. The study showed a combination of beta-carotene,
vitamin E, and selenium significantly reduced incidence of both gastric
cancer and cancer overall. (1)

Â• A 1994 cancer prevention study entitled the Alpha-Tocopherol
(vitmain E)/Beta-Carotene Cancer Prevention Study (ATBC)
demonstrated that lung cancer rates of Finnish male smokers increased
significantly with beta-carotene and were not affected by vitamin E. (2)

Â• Another 1994 study, the Beta-Carotene and Retinol (vitamin A)
Efficacy Trial (CARET), also demonstrated a possible increase in lung
cancer associated with antioxidants. (3)

Â• The 1996 Physicians' Health Study I (PHS) found no change in cancer
rates associated with beta-carotene and aspirin taken by U.S. male
physicians. (4)

Â• The 1999 Women's Health Study (WHS) tested effects of vitamin E
and beta-carotene in the prevention of cancer and cardiovascular
disease among women age 45 years or older. Among apparently healthy
women, there was no benefit or harm from beta-carotene
supplementation. Investigation of the effect of vitamin E is ongoing. (5)

Are antioxidants under investigation in current large-scale
clinical trials?
Three large-scale clinical trials continue to investigate the effect of
antioxidants on cancer. The objective of each of these studies is
described below. More information about clinical trails can be obtained
using cancer.gov/clinicaltrials, www.clinicaltrials.gov, or the CRISP
database at www.nih.gov.

Â• The Women's Health Study (WHS) is currently evaluating the effect of
vitamin E in the primary prevention of cancer among U.S. female health
professionals age 45 and older. The WHS is expected to conclude in
August 2004.

Â• The Selenium and Vitamin E Cancer Prevention Trial (SELECT) is taking
place in the United States, Puerto Rico, and Canada. SELECT is trying to
find out if taking selenium and/or vitamin E supplements can prevent
prostate cancer in men age 50 or older. The SELECT trial is expected to
stop recruiting patients in May 2006.

Â• The Physicians' Health Study II (PHS II) is a follow up to the earlier
clinical trial by the same name. The study is investigating the effects of
vitamin E, C, and multivitamins on prostate cancer and total cancer
incidence. The PHS II is expected to conclude in August 2007.

Will NCI continue to investigate the effect of beta-carotene
on cancer?
Given the unexpected results of ATBC and CARET, and the finding of no
effect of beta-carotene in the PHS and WHS, NCI will follow the people
who participated in these studies and will examine the long-term health
effects of beta-carotene supplements. Post-trial follow-up has already
been funded by NCI for CARET, ATBC, the Chinese Cancer Prevention
Study, and the two smaller trials of skin cancer and colon polyps. Post-
trial follow-up results have been published for ATBC, and as of July 2004
are in press for CARET and are in progress for the Chinese Cancer
Prevention Study.

How might antioxidants prevent cancer?
Antioxidants neutralize free radicals as the natural by-product of normal
cell processes. Free radicals are molecules with incomplete electron
shells which make them more chemically reactive than those with
complete electron shells. Exposure to various environmental factors,
including tobacco smoke and radiation, can also lead to free radical
formation. In humans, the most common form of free radicals is oxygen.
When an oxygen molecule (O2) becomes electrically charged or
"radicalized" it tries to steal electrons from other molecules, causing
damage to the DNA and other molecules. Over time, such damage may
become irreversible and lead to disease including cancer. Antioxidants
are often described as "mopping up" free radicals, meaning they
neutralize the electrical charge and prevent the free radical from taking
electrons from other molecules.

Which foods are rich in antioxidants?
Antioxidants are abundant in fruits and vegetables, as well as in other
foods including nuts, grains and some meats, poultry and fish. The list
below describes food sources of common antioxidants.

Â• Beta-carotene is found in many foods that are orange in color,
including sweet potatoes, carrots, cantaloupe, squash, apricots,
pumpkin, and mangos. Some green leafy vegetables including collard
greens, spinach, and kale are also rich in beta-carotene.

Â• Lutein, best known for its association with healthy eyes, is abundant
in green, leafy vegetables such as collard greens, spinach, and kale.

Â• Lycopene is a potent antioxidant found in tomatoes, watermelon,
guava, papaya, apricots, pink grapefruit, blood oranges, and other
foods. Estimates suggest 85 percent of American dietary intake of
lycopene comes from tomatoes and tomato products.

Â• Selenium is a mineral, not an antioxidant nutrient. However, it is a
component of antioxidant enzymes. Plant foods like rice and wheat are
the major dietary sources of selenium in most countries. The amount of
selenium in soil, which varies by region, determines the amount of
selenium in the foods grown in that soil. Animals that eat grains or
plants grown in selenium-rich soil have higher levels of selenium in their
muscle. In the United States, meats and bread are common sources of
dietary selenium. Brazil nuts also contain large quantities of selenium.

Â• Vitamin A is found in three main forms: retinol (Vitamin A1), 3,4-
didehydroretinol (Vitamin A2), and 3-hydroxy-retinol (Vitamin A3). Foods
rich in vitamin A include liver, sweet potatoes, carrots, milk, egg yolks
and mozzarella cheese.

Â• Vitamin C is also called ascorbic acid, and can be found in high
abundance in many fruits and vegetables and is also found in cereals,
beef, poultry and fish.

Â• Vitamin E, also known as alpha-tocopherol, is found in almonds, in
many oils including wheat germ, safflower, corn and soybean oils, and
also found in mangos, nuts, broccoli and other foods.

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References:
1)Blot WJ, Li JY, Taylor PR, et al. Nutrition intervention trials in Linxian, China:
supplementation with specific vitamin/mineral combinations, cancer incidence, and
disease-specific mortality in the general population. J Natl Cancer Inst 1993;85:
1483-91.

2)The Alpha-Tocopherol, Beta Carotene Cancer Prevention Study Group. The
effects of vitamin E and beta carotene on the incidence of lung cancer and other
cancers in male smokers. N Engl J Med 1994;330:1029-35.

3)Omenn GS, Goodman G, Thomquist M, et al. The beta-carotene and retinol
efficacy trial (CARET) for chemoprevention of lung cancer in high risk populations:
smokers and asbestos-exposed workers. Cancer Res 1994;54(7 Suppl):2038s-
43s.

4)Hennekens CH, Buring JE, Manson JE, Stampfer M, Rosner B, Cook NR, et al.
Lack of effect of long-term supplementation with beta carotene on the incidence
of malignant neoplasms and cardiovascular disease. N Engl J Med 1996;334:1145-
9.

5)Lee IM, Cook NR, Manson JE. Beta-carotene supplementation and incidence of
cancer and cardiovascular disease: Women's Health Study. J Natl Cancer Inst
1999;91:2102-6.

SOURCE Antioxidants and Cancer Prevention National Cancer Institute Online
Publication December 22, 2005

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